Parameters

Is is a valid host command-queue in which the read command will be
queued. command_queue and buffer
must be created with the same OpenCL context.

buffer

Refers to a valid buffer object.

blocking_read

Indicates if the read operations are blocking or
non-blocking.

If blocking_read is CL_TRUE i.e.
the read command is blocking, clEnqueueReadBufferRect
does not return until the buffer data has been read and copied into memory
pointed to by ptr.

If blocking_read is CL_FALSE
i.e. the read command is non-blocking,
clEnqueueReadBufferRect queues a non-blocking read
command and returns. The contents of the buffer that ptr
points to cannot be used until the read command has completed. The
event argument argument returns an event object which
can be used to query the execution status of the read command. When the read
command has completed, the contents of the buffer that ptr
points to can be used by the application.

buffer_origin

The (x, y, z) offset in the memory
region associated with buffer. For a 2D
rectangle region, the z value given by
buffer_origin[2] should be 0. The offset
in bytes is computed as buffer_origin[2] *
buffer_slice_pitch + buffer_origin[1]
* buffer_row_pitch + buffer_origin[0].

host_origin

The (x, y, z) offset in the memory region pointed to by
ptr. For a 2D rectangle region, the z
value given by host_origin[2] should be 0. The
offset in bytes is computed as host_origin[2] *
host_slice_pitch + host_origin[1]
* host_row_pitch + host_origin[0].

region

The (width in bytes, height in rows,
depth in slices) of the 2D or 3D rectangle
being read or written. For a 2D rectangle copy, the depth
value given by region[2] should be 1.
The values in region cannot be 0.

buffer_row_pitch

The length of each row in bytes to be used for the memory region associated
with buffer. If buffer_row_pitch
is 0, buffer_row_pitch is computed as
region[0].

buffer_slice_pitch

The length of each 2D slice in bytes to be used for the memory region associated
with buffer. If buffer_slice_pitch is 0,
buffer_slice_pitch is computed as region[1]
* buffer_row_pitch.

host_row_pitch

The length of each row in bytes to be used for the memory region pointed
to by ptr. If host_row_pitch is 0,
host_row_pitch is computed as region[0].

host_slice_pitch

The length of each 2D slice in bytes to be used for the memory region pointed
to by ptr. If host_slice_pitch
is 0, host_slice_pitch is computed as
region[1] * host_row_pitch.

ptr

The pointer to buffer in host memory where data is to be read into.

event_wait_list
, num_events_in_wait_list

event_wait_list
and num_events_in_wait_list specify events that
need to complete before this particular command can be executed.
If event_wait_list is NULL, then this particular command
does not wait on any event to complete. If event_wait_list
is NULL, num_events_in_wait_list must be 0. If
event_wait_list is not NULL, the list of events
pointed to by event_wait_list must be valid
and num_events_in_wait_list must be greater
than 0. The events specified in event_wait_list
act as synchronization points. The context associated with events in
event_wait_list and command_queue
must be the same. The memory associated with event_wait_list
can be reused or freed after the function returns.

event

Returns an event object that identifies
this particular read command and can be used to query or queue a wait
for this particular command to complete. event can be
NULL in which case it will not be possible for the application to query
the status of this command or queue a wait for this command to complete.
If the event_wait_list and the event arguments are
not NULL, the event argument should not refer to an
element of the event_wait_list array.

Notes

Calling clEnqueueReadBufferRect to read a region of the buffer
object with the ptr argument value set to host_ptr
and host_origin, buffer_origin
values are the same, where host_ptr is a pointer to the
memory region specified when the buffer object being read is created with
CL_MEM_USE_HOST_PTR, must meet the same requirements given for
clEnqueueReadBuffer:

All commands that use this buffer object or a memory object (buffer or image) created
from this buffer object have finished execution before the read command begins
execution.

The buffer object or memory objects created from this buffer object are not mapped.

The buffer object or memory objects created from this buffer object are not used
by any command-queue until the read command has finished execution.

Errors

clEnqueueReadBufferRect returns CL_SUCCESS if
the function is executed successfully. Otherwise, it returns one of the following errors:

CL_INVALID_COMMAND_QUEUE if command_queue
is not a valid host command-queue.

CL_INVALID_CONTEXT if the context associated with
command_queue and buffer are not the same
or if the context associated with command_queue and events in
event_wait_list are not the same.

CL_INVALID_MEM_OBJECT if buffer is not
a valid buffer object.

CL_INVALID_VALUE if the region being read
specified by (buffer_origin, region,
buffer_row_pitch, buffer_slice_pitch)
is out of bounds.

CL_INVALID_VALUE if ptr is a NULL value.

CL_INVALID_VALUE if any region array
element is 0.

CL_INVALID_VALUE if buffer_row_pitch
is not 0 and is less than region[0].

CL_INVALID_VALUE if host_row_pitch
is not 0 and is less than region[0].

CL_INVALID_VALUE if buffer_slice_pitch
is not 0 and is less than region[1] *
buffer_row_pitch and not a multiple of
buffer_row_pitch.

CL_INVALID_VALUE if host_slice_pitch is not
0 and is less than region[1] * host_row_pitch
and not a multiple of host_row_pitch.

CL_INVALID_EVENT_WAIT_LIST
if event_wait_list is NULL and
num_events_in_wait_list > 0,
or event_wait_list is not NULL and
num_events_in_wait_list is 0, or if event objects in
event_wait_list are not valid events.

CL_MISALIGNED_SUB_BUFFER_OFFSET if
buffer is a sub-buffer object and offset
specified when the sub-buffer object is created is not aligned to
CL_DEVICE_MEM_BASE_ADDR_ALIGN value for device associated
with queue.

CL_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST if the read
and write operations are blocking and the execution status of any of the events
in event_wait_list is a negative integer value.

CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to
allocate memory for data store associated with buffer.

CL_INVALID_OPERATION if
clEnqueueReadBufferRect is called on buffer
which has been created with CL_MEM_HOST_WRITE_ONLY or
CL_MEM_HOST_NO_ACCESS.

CL_OUT_OF_RESOURCES if there is a failure to allocate
resources required by the OpenCL implementation on the device.

CL_OUT_OF_HOST_MEMORY if there is a failure to allocate
resources required by the OpenCL implementation on the host.